Date-rape drugs and abuse of prescription medicine are on the rise, drugs monitoring agency INCB warned Wednesday, while pointing to an increasing number of illegal Internet pharmacies.

Date-rape drugs -- so called because they render victims unconscious or provoke memory loss, facilitating rape -- were increasingly easy to obtain, the International Narcotics Control Board said in its annual report Wednesday.

"The 'date-rape drug' phenomenon is evolving rapidly, as sexual abusers attempt to circumvent more rigorous drug controls by using substances not restricted by the international drug conventions," it noted.

Rohypnol, the best known date-rape drugs, is subject to strict checks, but others like GHB, ketamine, an anaesthetic, and GBL, a solvent, are becoming more and more common and are easily available through legal channels.

This is a "worrying" development, the Vienna-based agency said, calling on governments and drug-makers to raise awareness and introduce dyes and flavourings in these narcotics to make them more visible to potential victims.

Abuse of prescription drugs -- including morphine, codeine and methadone -- has also spread in recent years to become a "major concern" in many countries, with the number of users even surpassing the combined figure of cocaine, heroin and ecstasy users in places such as the United States, the INCB said.

"Almost all countries are confronted with trafficking in and abuse of prescription drugs ... in many countries, prescription drugs are the second or third most abused category of drugs," it said.

In parts of Europe, 15 percent of students were believed to use sedatives or tranquilisers without a prescription, the UN-affiliated agency said.

"Despite the fact that the abuse of prescription drugs is a fast-growing global problem, it continues to be difficult to obtain comprehensive data on the actual level of abuse of such drugs," it noted however.

Rarely associated with health risks, the non-medical use of pain medicine was "underreported and not adequately studied" and remained a "hidden problem," the board said.

A related issue was the emergence of illegal Internet pharmacies and telephone call centres -- many of them based in India -- allowing abusers to purchase drugs without a prescription, the INCB found.

This "puts consumers of those substances at an inordinate risk," board president Sevil Atasoy noted in the report, calling for governments to shut these services down.

Greater efforts must also be made to prevent drug abuse, in conjunction with non-governmental and community organisations, and to target vulnerable groups such as children and young people.

"Even a single early experience with drug abuse can have serious consequences, such as unintentional injury, overdose or arrest," Atasoy said.